2011 Ford V8/5.0 TT Package 3.73 31ft Cougar lite 7800 max

The 5.0 does not tow well at the limits of the truck, and I see you are in washington state. Elevation changes are not going to help things. I said it before and I'll say it again, I yanked around a 6400lb (loaded ready to go, yours is already @ 5900 with nothing in it) trailer with my previous 5.0 here in the adirondack/finger lake region. Not very fun with the elevation changes/climbs. That trailer is going to have quite a bit of influence on the truck as well, it weighs quite a bit more and it decently long. make sure you get a quality sway/wdh setup if youre going to do it anyways.

You said it yourself, the weights are close. Meaning you are at the limits of the truck. Are you comfortable with that? If so, let it rip. It's a free country.